There is available in the market today, glass substrates, such as large glass windows, which have a tin oxide coating on a selected surface thereof. The purpose of the tin oxide coating is to improve the emissivity value of the window over the emissivity value which it would have without a coating thereon. Normally, the emissivity value of a glass substrate, such as a window, is improved by the application of a tin oxide coating thereto. A clear glass window having a thickness of 1/8inch has an emissivity value of 0.84, whereas such a glass window coated with a tin oxide coating would have an emissivity value in a range of 0.50-0.35.
The lower the emissivity value, the better the coated glass substrate is in reflecting infrared radiation. For example, if such a coated glass substrate is glazed into a window, the coating is effective in reflecting back into the building the infrared radiation produced within the building as, for example, by means of a fuel burning furnace. Most of such infrared radiation would normally pass through an uncoated window, but will have a large proportion thereof reflected back into the building by a properly coated glass window.
The present-day practice for manufacturing such coated glass products is one in which a tin oxide coating is developed on a glass substrate by a pyrolytic application to a heated glass substrate of a coating material. In today's manufacturing processes, the coating material used is one which contains a chemical compound known as monobutyl tin trichloride (MBTC) in a suitable solvent. This chemical compound is sprayed in its dissolved form against a selected surface of a heated glass substrate in an oxidizing atmosphere. The result of such processing is that a coating of oxidized tin is developed on the selected surface of the glass substrate.
With respect to my knowledge of the known prior art, MBTC dissolved in a suitable solvent is the most efficient material known at the present time for the commercial spraying of glass substrates to develop a tin oxide coating thereon. By an efficient material, it is meant that this material, MBTC, will deposit more tin oxide per gram of sprayed tin than any other presently known tin oxide producing material will produce per gram of sprayed tin, assuming, of course, that the spraying conditions are the same for comparison purposes.
One object of my invention is to produce a glass substrate coated with tin oxide in which the glass substrate has a thicker coating of oxidized tin deposited thereon than can be deposited by previously used tin coating materials such as MBTC. It is another object of my invention to provide a method of making a glass substrate coated with tin oxide, which method has a higher efficiency in the formation of such a tin oxide coating on a glass substrate than can be achieved by the use of a method which employs previously known tin oxide producing materials such as MBTC.